The present invention relates to the drying of inks, lacquers, adhesives and the like, and more particularly to a drying arrangement for effecting such drying.
It is known, particularly from printing machines such as offset printing machines, that inks, lacquers, adhesives and similar substances which are applied on sheet material such as paper, cardboard, synthetic plastic foils or the like, must be dried during the travel of the sheet material through a machine, such as a printing machine. Equipment for this purpose exists in the art, and usually involves large drying apparatuses requiring the circulation of heated air. This equipment is very large and thus requires space which is often at a premium, it is complicated and expensive to produce and it requires almost constant servicing, all of which makes this prior-art equipment disadvantageous from an economic point of view.
In recent times substances have been developed, such as inks and the like, which cannot even be dried at all with the type of equipment mentioned above. These substances can be dried only by ultraviolet (UV) radiation, since the drying of the substances is based upon a polymerization action which takes place only when the substances are subjected to ultraviolet radiation of a certain intensity and wavelength. Since there are such substances in use, and have become very popular in the industry, the prior art has developed equipment for drying them. Thus, it is known from German Pat. No. 2,221,930 to provide a drying arrangement utilizing a source of UV radiation which is directed against the substances to be dried. One or more substantially tubular radiation sources extend transversely of the path of movement of the sheet material carrying the substance to be dried, and they are provided with reflectors which serve to direct all of the emitted UV radiation against the exposed surface or surfaces of the sheet material in order to dry the substance or substances thereon.
The difficulty with utilizing UV radiation for the drying of substances of the type outlined earlier on sheet materials is that it is impossible to produce UV radiation without at the same time also producing a significant amount of infrared (IR) radiation. The higher the value of the UV radiation, the higher the value of the incidentally produced infrared radiation. Infrared radiation, of course, means heat and this, in turn, brings with it the very substantial possibility that the sheet material, and even parts of the apparatus in which the drying arrangement is utilized, might become damaged by the significant amount of heat which is thus developed. The sheet material might, for instance, shrink, become excessively dry or might even burn or melt in the case of synthetic plastic foils.
The aforementioned German patent proposes to use a cooling arrangement for the radiation sources, in form of a blower which blows adjustable quantities of cooling air along the reflectors so as to carry off the undesired heat which should not reach the sheet material. The patent also realizes that under certain circumstances, for instance if the printing machine in which such a drying arrangement might be utilized, should malfunction and have to be stopped, the heat of the incidental IR radiation might become so great as to cause burning of the sheet material. To avoid this possibility, it is proposed to utilize flaps or baffles which in the event of machine malfunction are moved to a position in which they become interposed between the sheet material and the radiation source or sources, in order to protect the sheet material from direct radiation and possible damage.
This prior-art construction also is not fully satisfactory. On the one hand, it is expensive to produce since it is quite complicated. On the other hand, and even more importantly, it does not--despite the attempts made--preclude the possibility that the sheet material or parts of the surrounding equipment might become damaged due to heat. Even when the safety baffles are in place, the incidental IR radiation can cause heating of the safety baffles to temperatures of approximately 400.degree.C, and quite evidently these temperatures are sufficient to result in combustion of the sheet material even though the baffles are in place, since the distance at which the radiation source can be located from the sheet material (and hence the distance at which the interposed baffles can be spaced from the sheet material) is necessarily limited.
Moreover, the aforementioned prior-art arrangement cannot be used at all in certain applications. For instance, in printing machines in which individual sheets of material are engaged--usually by grippers of synthetic plastic material--to be transported along, this type of drying arrangement would heat the plastic grippers excessively and would cause damage to them.
Another drawback is the fact that in order to make the baffles tiltable to and from their closed positions, it is necessary that pivots be provided and arrangements for effecting the pivoting, and that they must all be located directly in the vicinity of the radiation source, so that they are subjected to the IR radiation. This means that only high-quality specialty materials can be employed for the manufacture of these components, and evidently this makes the prior-art arrangement even more expensive.